The present invention relates to backwashing fluid filters including differential-pressure sensors which sense when the filter body is overly clogged to initiate a backwashing operation for backwashing the fluid feed through the filter body while relative motion is effected between the filter body and a backwash nozzle provided in the filter. The present invention is particularly directed to the differential-pressure sensor included in such a backwashing filter for sensing the condition of the filter body and for controlling the initiation and termination of the backwashing operation. The invention is especially, but not exclusively, applicable to the differential-pressure sensor described in my patent application No. 114,894, and is therefore described below with respect to this application.
My above-cited patent application relates to a differential-pressure valve, and also to a system including a controlled device, such as a main valve, controlled by the differential-pressure valve. One use for such a valve and system, as mentioned in the above-cited patent application, is in backwashable filtering devices which are automatically actuated to backwash the filter whenever a predetermined quantity of dirt has accumulated on the filter as sensed by the differential-pressure valve sensing the difference in the pressure at points upstream and downstream of the filter body. When a backwashing operation is initiated, the backwash nozzle within the filtering device is connected to the atmosphere to produce a backwashing flow of the fluid through the filter body and out through the backwash nozzle. In addition, relative rotary movement is effected between the filter body and the backwash nozzle to cause the backwash nozzle to scan and clean the complete outer surface of the filter body.